Walfords sells a radio he calls a REGEN TRF.Can anyone here recommend any technical explanations how to build regen TRF radios? Transistors or tubes.Walfords does not publish his schematic for all to see and discuss so the only way you see that schematic is in his purchased kit.Which I did buy. But can't really discuss without sharing his protected schematic.So I was wondering if there was another regen TRF to discuss that is in public view.

I found a clearer schematic on 4sqrp web page....: ozarkpatrol_schematic.jpg

I was hoping to find an answer to the question of WHAT IS A REGEN TRF

I thought a TRF was a TUNED RADIO FREQUENCY circuit anda regenerative receiver was a different animal and thats why we call it a REGEN.

So where it gets weird is Walford calls his radio a "REGEN TRF".

The OZARKPATROL description says:The Ozark Patrol circuit is a two-band shortwave receiver, using only three NPN transistors in its circuit. It employs a reflexed regenerative detector to maximize gain from its simple design, followed by a two-transistor audio amp. It is capable of operating from a simple wire antenna.

Its not that I am looking for another regenerative receiver to build.I have built a few and made them available .... and gave away a bunch of them. http://www.learnmorsecode.com/regen/00regen.htmlI've heard France and Cuba on $6 home brewed radios.

The WALFORD ROCKWELL REGEN TRF is quite an oddball circuit compared tothe rest I have found on the internet. It uses four BS170 MOSFETs which I just learned was nearly the same as 2N7000 MOSFETS.....which I am more accustomed to using as on / off switching... not RF and audio amplification.

Here are some schematics of regen receivers which I have built using the Ozark receiver chassis as a test bed.

All use ferrite rod antennas the high Q of which is a necessity in some of the circuits which use the intrinsic Base-Emitter capacitance as one of the Colpitts feedback elements, about 10 turns to tune up to 10 MHz.

For an audio amplifier I frequently use a TL431 shunt regulator as shown in schematic 5.

First of all, a regens sensitivity to signals falls off greatly when it is taken out of oscillation. This is really pronounced when detecting AM signals. The receiver will be most sensitive when just starting to oscillate. Old time hams were aware that a regen was hard to beat for code, but for AM they are more deaf ( weak signal work). A tuned front end ahead of a regen will be comparable to a good superhet in detecting AM signals. An untuned front end has the same effect, but suffers from some of its own problems.

A tuned front end works better at eliminating station "break through". This is where a strong station close in frequency occupies 100khz or so on the dial and is untunable.

Untuned front ends can suffer from several problems. First is it can actually act as a detector itself, passing this audio through to the next stage. Second it can be easily overloaded by nearby stations and cause IMD. Third, when biased properly to prevent "detection" current draw goes up.

Perusing old SW Craft magazines you will find many designs with tuned front ends ahead of a regen detector. Also I think there were military versions that used the same configuration. If I believe properly, the National SW3 has a tuned front end ahead of its regen detector.

You can see it does well on the AM ham stations, I would say if it were just a straight regen, those AM signals would be down in the "mud". They had two modes back then. CW and " AM Phone". The tuned RF stage helped out tremendously on "phone".

In particular, scroll down to An Analysis of AC Operated Shortwave Receiver Design

RF stages must be properly shielded and screened, otherwise signals will find their way around the RF amp and into the detector. Details can be found in radio HBs from the 1930s, both the ARRL and E&E. Finding the sort of ganged VCs that Millen used is very difficult today. While the RF amp can be tuned separately from the detector, RF tuning will affect regeneration level and vice versa. It does take a bit of fiddling to tune in a station. I actually don't mind that, but it certainly isn't a superhet kind of tuning experience. Rather than use an RF stage, I've come to prefer simply zero-beating the detector with an AM station. Of course, the tuning has to be precise enough, the detector stabile enough to do this.

I think the 'secret' to using a regen well is the RF attenuator between the antenna and the detector or RF stage. Keep the incoming RF level as low as possible without losing the signal in the noise. Strong signals force you to back down on regeneration and that worsens selectivity and sensitivity. Make up the gain in the audio section.

An observation on regen AM sensitivity: about the same as a pentagrid converter (eg, 12BE6), so adequate up to at least 7 or 8MHz. At my present noisy location, a pentagrid front end is good to almost 12MHz!

I didn't make my point very clearly. I'll try again. But first, I emphasize that this is just my preferred way of using a regen. A description, not a prescription.

Regen selectivity is all on the nose, the bandpass skirts are wide. Triangle shape rather than the box shape of a good filter. You get the best results when the incoming RF level is adjusted (ie, attenuated) to keep signals as close as possible to that nose, and away from the skirts.

The first step is to adjust the RF attenuator so that touching the antenna lead to the receiver just slightly increases noise level. You leave it there (for a given band and time); occasionally really strong signals will force you reduce RF level even more. This is standard practice for communication receivers: set the RF gain or the attenuator so that incoming noise off the antenna slightly exceeds the receiver's own generated noise level.

Of course doing this reduces the audio volume level, but the signal to noise ratio will be as good as it can get. You make up for the lower volume with more audio amplification, rather than reducing RF attenuation.

I bought it.I built it.I heard the world.EVERYBODY should build a handful of these and just hand them out to kids....or build them with the kids.This WALFORDS ROCKWELL REGEN-TRF should be every kids first radio... just like we thought of crystal radios in our youth.I'm impressed.schematic is here:http://www.learnmorsecode.com/regen/WALFORDS/index.html

Although this receiver appears to use a 2 gang capacitor, both gangs are in parallel for the lower band and only one gang is used for the upper band.

The RF amplifier is untuned and followed by a tuned Colpitts oscillator.

Does this mean that it is truly a TRF Regen receiver????

The use of Mosfets interests me. They have a very large input capacitance (60pF) which will likely limit them to use in the lower shortwave bands but instead of being a disadvantage this intrinsic Gate-Source capacitance can likely be used as the feedback capacitors in a Colpitts oscillator circuit such as the modified circuit shown below with TR3 acting as the detector.

Because I like simple and because my experience has been that with a ferrite rod antenna no RF stage or external antenna are necessary for most shortwave listening, my intention is to try the simplified second circuit below.

I don't know with the values shown whether the biasing will be correct for the detector FET if the oscillator and detector FETs are direct coupled, but if not, the detector FET can be capacitively coupled and biased as shown in the modified first schematic.